The drilling, completion and production of a plurality of wells in a single area under water has been accomplished in a number of cases in recent years. Thus, in the North Sea Argyll Field, a plurality of subsea satellite wells were installed in the vicinity of a subsea manifold station connected via a production riser to a semi-submersible surface vessel containing equipment for processing crude oil, the staellite wells being connected to the subsea manifold station by remotely installed flowlines. While such prior-art procedures, and the apparatus employed, have achieved considerable success, they have had a number of disadvantages, including the relatively high cost of drilling and completing satellite wells, the relative complexities arising from a plurality of unitary subsea installations, one for each satellite and one for the manifold station, and particularly the difficulties and cost involved in laying flowlines from each satellite well to the manifold station.
As an alternative approach to drilling a number of underwater wells independently, prior-art workers have proposed to employ templates including both means for establishing a plurality of wells, by drilling through the template, and means for connecting the completed wells to flowline portions carried by the template structure. Typical of such proposals are the apparatus disclosed in the following U.S. Pat. Nos.:
3,004,612: Kofahl PA1 3,633,667: Falkner PA1 3,877,520: Putman
Though such proposals have the advantage of concentrating the wellheads for a plurality of underwater wells in a small area, they provide little aid with respect to the problem of handling the fluid produced from the wells.
There has accordingly been a continuing need for improvement in both the overall approach to drilling, completing and producing multiple underwater wells and apparatus for accomplishing those ends.